Balanced mixer utilizing strip transmission line hybrid

ABSTRACT

A microwave hybrid in a strip transmission line configuration is provided. Two narrow striplike conductors are joined together to form a T-configuration. Another narrow striplike conductor is positioned parallel to one of the conductors along the crossed portion of the T-configuration. A ground plane is placed to form with the narrow striplike conductors a plurality of transmission lines for propagating signal energy in an electromagnetic mode.

[111 3,6]1Lll53 lnventor Cheng lloul Wen Trenton, NJ.

Appl. No. $76,001

Filed Nov. 12, 11969 Patented Oct. 5, 1971 Assignee RCA CorporationBALANCED MIXER UTllLllZlNG STRIP TRANSMHSSIION LINE HYBRID [56]References Cited UNITED STATES PATENTS 3,310,748 3/1967 Putnam 325/4463,451.015 6/1969 Heath r v 333/84(M)X Primary Examiner-Herman KarlSaalbach Assistant Examiner-Paul L. Gensler Attorney-Edward J. NortonABSTRACT: A microwave hybrid in a strip transmission line configurationis provided. Two narrow striplike conductors 8 Claims 3 Drawing Figs arejoined together to form a T-configuration. Another narrow US. Cl325/446, striplilge conductor is positioned parallel to one of theconduc- 333/10, 333/11, 333/84 M tors along the crossed portion of theT-configuration. A Int. Cl l1-ll04b 1/26 ground plane is placed to formwith the narrow striplike con- Field of Search 333/10, 1 1, ductors aplurality of transmission lines for propagating signal 84 M; 325/446energy in an electromagnetic mode.

40 4 43 L.O. i

37: 33 [II 7 :5 Z: s9 2l I '5 Mill 2?) V- IN [V MIXER l i l 5- I l 29mm/ll A |J| ll 1 GROUND PLANE l GROUND PLANE BALANCED MIXER UTILIZINGSTRIP TRANSMISSION LINE HYBRID This invention relates to microwavehybrid circuits and more particularly to a hybrid configurationemploying strip transmission lines.

In the prior art, large and bulky microwave hybrids such as magic teesin waveguide and coaxial systems are known. These forms of hybrids,because of their size and structure, are not compact and do not adapteasily to microwave integrated circuit configurations. The most widelyused microwave integrated circuit configuration includes a singlesubstrate of dielectric material having a ground plane on one sidethereof and a narrow striplike conductor on the opposite side. There isa new form of microwave integrated circuit proposed wherein the groundplane and the narrow striplike conductor are both on the same surface orside of the dielectric substrate. This new type of transmission line isdescribed by the applicant C. P. Wen in lEEE 1969 G-M'l'l" internationalMicrowave Symposium Digest of May 1969 under the title A Surface StripTransmission Line Suitable for Nonreciprocal Gyromagnetic DeviceApplications."

Large waveguide magic tees or coaxial systems are difficult to couple toeither of these above configurations and also add a great deal of bulkand weight that integrated circuits are intended to avoid. Althoughthere exists a distributed-circuittype magic tee, the operatingbandwidth of the distributed-circuit type is limited because of theone-quarter wavelength requirement imposed on thedistributed-circuit-type magic tee.

It is therefore an object of the present invention to provide animproved microwave hybrid which is low cost, compact and adaptable foruse with microwave integrated circuit configurations.

This and other objects are accomplished by at least two narrow striplikeconductors fixed to one surface of a dielectric substrate. A first ofthe narrow striplike conductors is joined at a point along the second ofthe narrow striplike conductors. A substantially wider ground planarconductor is positioned on the dielectric to provide with the narrowstriplike conductors a plurality of transmission lines for propagatingsignals in an electromagnetic mode. The second of the narrow striplikeconductors is substantially in a straight line in the region of thejunction thereof with the first narrow striplike conductor. A thirdnarrow striplike conductor is fixed to the same surface of thedielectric as the other narrow striplike conductors. This third narrowstriplike conductor is positioned so that a portion thereof is closelyspaced and parallel to the substantially straight portion of the secondnarrow striplike conductor, whereby signals coupled to one end of thefirst narrow striplike conductor propagate in phase along the secondnarrow striplike conductor joined thereto and no appreciable signal iscoupled to the third narrow striplike conductor. Signals coupled to thethird narrow striplike conductor propagate towards each end of thesecond narrow striplike conductor with little or no coupling of thesignals to the first narrow striplike conductor.

A further description follows along with the accompanying drawingwherein:

FIG. 1 is a balanced mixer using a microwave hybrid in accordance with afirst embodiment of the present invention,

FIG. 2 is a microwave hybrid in accordance with a second embodiment ofthe present invention, and

FIG. 3 is a microwave hybrid in accordance with a third embodiment ofthe present invention.

Referring now to the particular microwave hybrid shown in FIG. 1, adielectric substrate 11 is provided, having a plurality of narrowstriplike conductors 13, 17 and 33 thereon. The first narrow striplikeconductor 13 on one surface of the substrate 11 is joined along itsmidpoint at point 15 to the second narrow striplike conductor 17 in amanner to form a T-shaped configuration. Substantially wider groundplanar conductors 29 and 31 are placed on the same surface of thedielectric substrate 11 to form with the narrow striplike conductor 17 acoplanar strip transmission line. This form of coplanar striptransmission line or surface strip transmission line is described inapplication Ser. No. 787,349 filed Dec. 27, 1969, now US. Pat. No.3,560,893, by applicant Cheng Paul Wen. This type of transmission linehas also been described by the applicant as mentioned above in theDigest of the IEEE International Microwave Symposium; Dallas, Tex.; May,1969.

A third narrow striplike conductor 33 is fixed to the same surface ofthe substrate 11. This third narrow striplike conductor 33 has oppositeend portions 35 and 37 substantially parallel to one another with amiddle portion 39 parallel and closely spaced in aligned relationshipwith the narrow striplike conductor 13. The narrow striplike conductor33 is positioned such that end portions 35 and 37 are aligned in adirection orthogonal to the narrow striplike conductor 13 with the endsof these portions 35 and 37 being equally spaced from the junction 15 ofnarrow striplike conductors 17 and 13.

If it is desired to use the hybrid arrangement to provide a balancedmixer configuration, one end or port 19 of transmission line 13 iscoupled to a diode mixer 23 and the opposite end 21 of transmission line13 is coupled to a second diode mixer 25. The free end 27 oftransmission line 17 is coupled to a source of RF (radio frequency)carrier signal energy, not shown, and a local oscillator 41) is coupledacross portions 35 and 37 of narrow striplike conductor 33.

In the operation of the balanced mixer arrangement shown in FlG. l,signals such as RF signals received at port 27 at one end of narrowstriplike conductor 17 propagate in the coplanar transmission line madeup of narrow striplike conductor 17 and ground planar conductors 29 and31 to the junction 15 of the narrow striplike conductor 13 and conductor17. At this point, the power of the: applied RF signal divides equallyand in phase and propagates along the transmission line formed by thenarrow striplike conductor 13 and ground planar conductor 31 to mixer 25at port 21 and propagates along the transmission line formed by thenarrow striplike conductor 13 and ground planar conductor 29 to mixer 23at port 19. If the lengths from junction 15 to mixers 25 and 23 areequidistant, the signal levels arriving at the respective mixers areequal and the signals are in phase. Although the narrow striplikeconductor 33 is spaced a short distance from conductor 13, little or nocoupling is provided to narrow striplike conductor 33 because the phaseof the applied RF signal is the same at opposite ends of the T-junction15 of narrow striplike conductor 13.

If, as suggested above, a local oscillator is coupled across the ends 41and 413 ofconductor 33 or at port 40 of the hybrid, the signals from thelocal oscillator at port 40 travel along the parallel narrow striplikeportions 35 and 37 in the manner of a parallel-conductor transmissionline with a shorted portion 39 parallel to the narrow striplikeconductor 13. At this shorted region 39, coupling of the localoscillator signal is provided to the narrow striplike conductor 13.Since the portions 35 and 37 of the parallel-conductor transmission lineare at opposite ends of narrow striplike conductor 13 with respect tojunction 15, the local oscillator signals are coupled to transmissionline 13 with the signal at one end of conductor 13 being out of phasewith respect to the signal at the other end and little or no coupling ofthe oscillator signal to the narrow striplike conductor 17 at the center15 of conductor 13 occurs. By providing the arrangement describedherein, one mixer is responsive to the input RF carrier and a localoscillator signal 180 out of phase with respect to the oscillator signalat the other mixer. It is known that when combiningthe mixer outputsignals, even order harmonic distortion from the local oscillator issuppressible.

A microwave hybrid in accordance with another embodiment of the presentinvention is shown in H6. 2. The narrow striplike conductor 53 issubstantially the same as narrow striplike conductor 33 in FIG. 1. lnthe arrangement of FIG. 2, the narrow striplike conductors 55 and 57, aswell as the conductor 53, are placed on one surface of the dielectricsubstrate 51 in much the same manner as conductors 13 and 17 of FIG.

l. The opposite surface of the dielectric substrate is provided with aground planar conductor 52. The narrow striplike cond uctors 55 and 57provide with ground planar conductor 52 two microstrip transmissionlines propagating microwave signal energy in the approximate transverseelectromagnetic (TEM)I'J'IOdg; Conductor 57 is joined at the middle ofconductor 55 at point 61 'to form a T-configuration of two transmis sionlines. The narrow striplike conductor 53 is positioned so that at thecoupling and termination region, portion 59 is closely spaced andparallel-to the conductor 55 so as to be in the electromagnetic couplingregion of narrow striplike conductor 55.

The operation of the configuration shown in FIG. 2 is like that ofFIG. 1. Signals traveling along narrow striplike conductor 57 are powersplit and arrive at opposite ends 56 and 58 of narrow striplikeconductor 55 in phase with little or no appreciable coupling to thenarrow striplike conductor 53. Signals coupled across the ends of narrowstriplike conductor 53 are coupled across the closely spaced region ofconductors 55 and 59 to the opposite ends 56 and 58 of narrow striplikeconductor 55. The power of a signal applied across the ends of conductor53 divides and appears at the opposite equidistant ends of the narrowstriplike conductor 55 180 out of phase. No appreciable coupling to thenarrowstriplike conductor 57 occurs.

A narrow band microwave hybrid is provided by a third embodiment of thepresent invention shown in FIG. 3. In FIG. 3 there is provided adielectric substrate 7 l with a ground planar conductor 73 on onesurface of substrate 71. Again two narrow striplike conductors 75 and 76are joined together at junction point 74 such as to form aT-configuration with narrow striplike conductor 76 at the midpoint ofnarrow striplike conductor 75. Narrow striplike conductor 75 and theground planar conductor 73 provide a transmission line which propagatessignals in a transverse electromagnetic (TEM) mode. Likewise signals arepropagated in the transverse electromagnetic (TEM) mode between thenarrow striplike conductor 76 and ground planar conductor 73.

A one-half wavelength resonator section 70 which is open circuited atboth ends is closely spaced adjacent to narrow striplike conductor 75.The resonator section 70 is formed of narrow striplike conductor 77 andthe ground planar conductor 73. The narrow conductor 77 is placed withrespect to the narrow striplike conductor 75 such that the center 78 ofthe narrow conductor 77 is adjacent to the junction 74. A narrowstriplike conductor 79 is spaced a short distance from one end 81 ofnarrow striplike conductor 77 so as to be in capacitycouplingrelationship with narrow strip conductor 77. A narrow band mixer isprovided by positioning mixer diodes, not shown, at the ends 85 and 87of narrow striplike conductor 75. An RF carrier signal is applied to thefree end 89 of the conductor 76. A local oscillator signal is applied tothe end 91 of the conductor 79.

In the operation of the hybrid as a balanced mixer, RF carrier signalsapplied between narrow striplike conductor 76 and ground conductor 73 atpoint 89 are propagated along the transmission line comprising narrowstriplike conductor 76 and ground planar conductor 73 to the junction74. At this point as per the previous arrangements, the RF carriersignal divides and appears at the equidistant points 87 and 85 in phasewith little or no coupling to the narrow strip 77 because, as in theprevious embodiments, the phase of the signal is the same at theopposite equidistant points from the junction 74.

The combination of the narrow striplike conductor 79, ground planarconductor 73 and the resonant narrow strip conductor 77 in thearrangement described, provides a form of directional coupler. If thelength of the resonator section 70. composed of narrow conductor 77 andground conductor 73 is one-half wavelength at the local oscillatorfrequency, oscillator signals applied at point 91 of narrow striplikeconductor 79 are capacitively coupled to the narrow striplike conductor77. The local oscillator signals are coupled from the striplikeconductor 77 to the closely spaced narrow striplike conductor 75. Thelocal oscillator signals arrive at opposite ends 87 and 85 of narrowstriplike conductor 75, l80 out of phase with respect to each other.This difference in phase and the fact that little or no coupling isprovided to conductor 76 results from the location of junction 74 ofnarrow striplike conductors 75 and 76 at the midpoint 78 of the one-halfwavelength along conductor 77.

What is claimed is:

l. A hybrid comprising in combination:

a dielectric substrate,

a first narrow striplike conductor fixed to one surface of saidsubstrate, a second narrow striplike conductor joined along a portion 15 of its length to one end of said first narrow striplike conductor in amanner to form three conductors radially extending from the junction ofsaid first and second conductors, said second narrow striplike conductorfixed to said one surface of said dielectric substrate,

2 relatively broad conductive means spaced with respect to said firstand second narrow striplike conductors to form with said first andsecond narrow striplike conductors three transmission lines radiallyextending from said junction, said lines being arranged for propagatingsignals in an electromagnetic mode, whereby first signals received atone end of said first narrow striplike conductor propagate in phasetoward opposite ends of said second narrow striplike conductor,

a third narrow striplike conductor fixed to said one surface of saidsubstrate with a portion of said third conductor closely spaced andparallel to the portion of said second conductor in the region of thejunction of said first and second conductors so as to beelectromagnetically coupled to each other,

means by which second signals are applied to said third conductor tocause said second signals coupled therefrom to said second conductor topower divide and propagate said second signals to the opposite ends ofsaid second conductor 180 out of phase without any significant couplingof said second signals from said second conductor to said firstconductor.

2. The combination as claimed in claim 1 wherein said conductive meansis a wide ground planar conductor fixed to the surface of said substrateopposite that to which said narrow striplike conductors are fixed.

3. The combination as claimed in claim 1 wherein said conductive meansincludes at least two ground planar conductors fixed to the same surfaceof said substrate as said striplike conductors.

4. The combination as claimed in claim 1 wherein the mid point of thelength of said third conductor is at a point adjacent to said region ofsaid junction of said first and second conductors.

5. The combination as claimed in claim 1 wherein said lastmentionedmeans comprises a parallel-conductor transmission line terminated bysaid third conductor connected across the parallel-conductortransmission line.

6. The combination as claimed in claim 2 wherein said third conductor isabout one-half wavelength long at the midoperating frequency of saidpropagating therealong.

7. The combination as claimed in claim 6 wherein said lastmentionedmeans comprises a fourth narrow striplike conductor with one end closelyspaced to one end of said third narrow striplike conductor.

8. A balanced mixer responsive to an RF microwave signal and a locallygenerated microwave signal comprising in combination:

a substantially flat dielectric substrate,

a first narrow striplike conductor fixed to one surface of saidsubstrate,

a second narrow striplike conductor joined along a portion of its lengthto said first conductor in a manner to form three radially extendingconductors extending from the junction of said first and secondconductors. said second narrow conductor fixed to said one surface ofsaid dielectric substrate,

relatively broad conductive means spaced with respect to said first andsecond conductors to form with said first and second conductors threeradially extending transmission lines for propagating said microwavesignals in an electromagnetic mode,

a first mixer coupled to one end of said second conductor,

a second mixer coupled to the opposite end of said second conductor,

the transmission line formed by said first conductor and said conductivemeans serving to support said RF microwave signal which is power dividedat the junction of said first and second conductors and fed in phase tosaid first and second mixer at opposite ends of said second conductor,

a third narrow striplike conductor fixed to said one surface of saidsubstrate with a portion of said third conductor closely spaced andparallel to the portion of said second conductor in the region of thejunction of said first and second conductors so as to beelectromagnetically coupled to each other, and

means by which said locally generated microwave signals are applied tosaid third conductor to cause said locally generated signals coupledtherefrom to said second conductor to power divide and propagate saidlocally generally signals to the opposite ends of said second conductorout of phase without any significant coupling of said locally generatedsignals to said first conductor.

1. A hybrid comprising in combination: a dielectric substrate, a firstnarrow striplike conductor fixed to one surface of said substrate, asecond narrow striplike conductor joined along a portion of its lengthto one end of said first narrow striplike conductor in a manner to formthree conductors radially extending from the junction of said first andsecond conductors, said second narrow striplike conductor fixed to saidone surface of said dielectric substrate, relatively broad conductivemeans spaced with respect to said first and second narrow striplikeconductors to form with said first and second narrow striplikeconductors three transmission lines radially extending from saidjunction, said lines being arranged for propagating signals in anelectromagnetic mode, whereby first signals received at one end of saidfirst narrow striplike conductor propagate in phase toward opposite endsof said second narrow striplike conductor, a third narrow striplikeconductor fixed to said one surface of said substrate with a portion ofsaid third conductor closely spaced and parallel to the portion of saidsecond conductor in the region of the junction of said first and secondconductors so as to be electromagnetically coupled to each other, meansby which second signals are applied to said third conductor to causesaid second signals coupled therefrom to said second conductor to powerdivide and propagate said second signals to the opposite ends of saidsecond conductor 180* out of phase without any significant coupling ofsaid second signals from said second conductor to said first conductor.2. The combination as claimed in claim 1 wherein said conductive meansis a wide ground planar conductor fixed to the surface of said substrateopposite that to which said narrow striplike cOnductors are fixed. 3.The combination as claimed in claim 1 wherein said conductive meansincludes at least two ground planar conductors fixed to the same surfaceof said substrate as said striplike conductors.
 4. The combination asclaimed in claim 1 wherein the midpoint of the length of said thirdconductor is at a point adjacent to said region of said junction of saidfirst and second conductors.
 5. The combination as claimed in claim 1wherein said last-mentioned means comprises a parallel-conductortransmission line terminated by said third conductor connected acrossthe parallel-conductor transmission line.
 6. The combination as claimedin claim 2 wherein said third conductor is about one-half wavelengthlong at the midoperating frequency of said propagating therealong. 7.The combination as claimed in claim 6 wherein said last-mentioned meanscomprises a fourth narrow striplike conductor with one end closelyspaced to one end of said third narrow striplike conductor.
 8. Abalanced mixer responsive to an RF microwave signal and a locallygenerated microwave signal comprising in combination: a substantiallyflat dielectric substrate, a first narrow striplike conductor fixed toone surface of said substrate, a second narrow striplike conductorjoined along a portion of its length to said first conductor in a mannerto form three radially extending conductors extending from the junctionof said first and second conductors, said second narrow conductor fixedto said one surface of said dielectric substrate, relatively broadconductive means spaced with respect to said first and second conductorsto form with said first and second conductors three radially extendingtransmission lines for propagating said microwave signals in anelectromagnetic mode, a first mixer coupled to one end of said secondconductor, a second mixer coupled to the opposite end of said secondconductor, the transmission line formed by said first conductor and saidconductive means serving to support said RF microwave signal which ispower divided at the junction of said first and second conductors andfed in phase to said first and second mixer at opposite ends of saidsecond conductor, a third narrow striplike conductor fixed to said onesurface of said substrate with a portion of said third conductor closelyspaced and parallel to the portion of said second conductor in theregion of the junction of said first and second conductors so as to beelectromagnetically coupled to each other, and means by which saidlocally generated microwave signals are applied to said third conductorto cause said locally generated signals coupled therefrom to said secondconductor to power divide and propagate said locally generally signalsto the opposite ends of said second conductor 180* out of phase withoutany significant coupling of said locally generated signals to said firstconductor.